This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "VLF cable testing" – news · newspapers · books · scholar · JSTOR(May 2012) (Learn how and when to remove this message)
VLF cable testing (Very Low Frequency) is a technique for testing of medium and high voltage (MV and HV) cables. VLF systems are advantageous in that they can be manufactured to be small and lightweight; making them useful – especially for field testing where transport and space can be issues. Because the inherent capacitance of a power cable needs to be charged when energised, system frequency voltage sources are much larger, heavier and more expensive than their lower-frequency alternatives. Traditionally DC hipot testing was used for field testing of cables, but DC testing has been shown to be ineffective for withstand testing of modern cables with polymer based insulation (XLPE, EPR). DC testing has also been shown to reduce the remaining life of cables with aged polymer insulation.[1]
VLF testing of cables is supported in IEC 60502 (up to 35 kV) and in IEEE 400.2 (up to 69 kV). As higher voltage VLF equipment is developed, standards may be adapted to increase the voltage level for application.
The VLF test can be used in a number of ways:
Apply VLF to cables in a simple withstand approach to detect potential failures (faults) in the cable insulation during a planned outage. The tested cable must withstand an AC voltage for a specified testing time without flashover. This method yields a "pass/fail" statement. VLF cable testing uses different wave shapes, typically sine and square and care must be taken when describing the voltage to be used. RMS and peak voltages have different relationships to each other depending on the wave shape and IEEE 400.2 uses the peak voltage level to equate the wave shapes. Frequency ranges used are within the range of 0.01 Hz to 0.1 Hz, where frequency selection depends on the load presented by the cable. Test voltage levels are either calculated using a multiple of the cable's nominal phase-phase voltage or via tables in IEEE 400.2; typically they are in the range of 1.5 U0 to 3 U0. The VLF cable testing time varies from 15 to 60 minutes. IEEE 400.2 establishes some suggested test voltages and times. Subsequent work by the CDFI has shown there to be no significant change in the efficacy of a VLF test conducted over the frequency range 0.1 to 0.01 Hz when the IEEE 400.2 voltages and times are used.[2]
Apply VLF to cables in a monitored withstand approach where a diagnostic measurement is made before and during the course of the withstand test. Monitoring a diagnostic enables some additional decision making before the final test voltage is reached. Some cables are not good candidates for withstand testing and a diagnostic indication obtained at a lower voltage can negate the need to perform withstand testing. During the test measurement of a diagnostic parameter can be used to optimise test times. Test times can be shortened for cables with good diagnostic indications or lengthened for cables that show deteriorating diagnostic measurements during the test.
Apply VLF to measure insulation losses (i.e. the insulation dissipation factor or Tan-delta). In this case, the IEEE 400.2 establishes the criteria for assessment. The test is typically performed over a range of test voltages from 0.5 Uo to 2 Uo depending on the standard/guide that is being followed.
Apply VLF in order to detect and measure partial discharge. In this case, the IEEE 400.3 outlines a procedure for assessment and IEC 60270 provides the background for partial discharge testing of high voltage apparatus. The test is typically performed over a range of test voltages to identify the different defects and their inception and extinction voltages.
^Srinivas, N.N; Duffy, E.K.; Starrett, W. (January 1993). "Effect of dc testing on extruded cross-linked polyethylene insulated cables". EPRI. OSTI 6688245. {{cite journal}}: Cite journal requires |journal= (help)
^Hampton, N.; Hernandez-Mejia, J.C.; Kuntsevich, M.; Perkel, J.; Tomer, V. "Estimating the Impact of VLF Frequency on Effectiveness of VLF Withstand Diagnostics". NEETRAC, Atlanta, USA.
VLFcabletesting (Very Low Frequency) is a technique for testing of medium and high voltage (MV and HV) cables. VLF systems are advantageous in that they...
test should an inadvertent discharge or breakdown occur. Burn-in Dielectric loss Electrical breakdown Electrical isolation test Impulse generator VLF...
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km,...
The VLF Transmitter Cutler is the United States Navy's very low frequency (VLF) shore radio station at Cutler, Maine. The station provides one-way communication...
Wiring Board (PWB) Design Definition of frequency bands (VLF, ELF … etc.) IK1QFK Home Page (vlf.it) Radio, light, and sound waves, conversion between wavelength...
and preceded the 1962 Soviet nuclear tests series. The K project nuclear testing series were all high altitude tests fired by missiles from the Kapustin...
low frequency (VLF) radio waves can penetrate seawater just over one hundred feet (30 metres), and many navies use powerful shore VLF transmitters for...
penetrate. Waves in the VLF range of 3 kHz to 30 kHz can penetrate to a depth of about 10 to 30 meters, and since WWII navies have used VLF transmitters to communicate...
length of the so-called Pittsburgh cable (the test was actually in Boston, the cable had previously been used for testing in Pittsburgh) on 6 September 1899...
faulty) of the cable under test. To measure the level of partial discharges, 50–60 Hz or sometimes a sinusoidal 0.1 Hz VLF (very low frequency) voltage...
decreases, so very low frequency (VLF) to extremely low frequency (ELF) ground waves can be used to communicate worldwide. VLF to ELF waves can penetrate significant...
used by Federal agencies, such as most NDBs, LORAN-C transmission towers or VLF transmission facilities of the US Navy, or about most towers not used for...
bandwidth (9 kHz) to transmission frequency is high. Diplexers are not used at VLF transmitters. In this frequency range their realization is very difficult...
VLAN—Virtual Local Area Network VLSM—Variable Length Subnet Mask VLB—Vesa Local Bus VLF—Very Low Frequency VLIW—Very Long Instruction Word VLSI—Very-Large-Scale...
States Navy. Cable companies are planning to use the band for wireless broadband in rural areas, with Charter Communications beginning tests of the service...
2018-06-05. U.S. cable television channel frequencies Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it)....
submarines. Unlike higher frequency radio waves, the very low frequency (VLF) waves generated by the alternator transmitters could penetrate seawater...
therefore are cut off from communication with military command authorities. VLF radio waves can penetrate 50–75 feet into seawater and have been used since...
their XR311 prototype and offered it for testing in 1970. At least a dozen of these were built for testing under the High Mobility Combat Vehicle, or...
emergency frequency (225–400 MHz) AM, including HAVE QUICK, dGPS RTCM-104 Cable television, though not transmitted aerially, uses a spectrum of frequencies...
Slovakia Former names VIP Air and VIP Wings DHE DAP Helicopteros HELIDAP Chile VLF DFS UK Limited VOLANTE United Kingdom WD DSR DAS Air Cargo DAIRAIR Uganda...
depth where VLF signals can reach. A submarine also has the option of floating a long, buoyant wire antenna to a shallower depth, allowing VLF transmissions...
one-way, since the long antennas needed to transmit VLF or ELF waves cannot fit on a submarine. VLF transmitters use miles long wire antennas like umbrella...
Pennsylvania and driven to Camp Holabird, Maryland on September 23 for Army testing. The vehicle met all the Army's criteria except engine torque. The Army...
Global Information